The present invention relates generally to herbicidal compositions or formulations, and to methods of using such compositions to kill or control the growth and proliferation of unwanted plants. In particular, the present invention relates to herbicidal compositions, as well as their methods of use, which comprise N-phosphonomethylglycine (glyphosate), or a herbicidal derivative thereof, and an auxin herbicide, or a herbicidal derivative thereof, optionally with one or more suitable surfactants. Such compositions cause early visual symptoms of treatment and/or enhanced effectiveness or control when applied to the foliage of plants.
Glyphosate is well known in the art as an effective post-emergent foliar-applied herbicide. In its acid form, glyphosate has a structure represented by the formula:
and is relatively insoluble in water (1.16% by weight at 25° C.). For this reason it is typically formulated as a water-soluble salt.
Among the water soluble salts of glyphosate is the potassium salt, having a structure represented by the formula:

in the ionic form predominantly present in aqueous solution at a pH of about 4. Glyphosate potassium salt has a molecular weight of 207. This salt is disclosed, for example, by Franz in U.S. Pat. No. 4,405,531, as one of the “alkali metal” salts of glyphosate useful as herbicides, with potassium being specifically disclosed as one of the alkali metals, along with lithium, sodium, cesium and rubidium. Example C discloses the preparation of the monopotassium salt by reacting the specified amounts of glyphosate acid and potassium carbonate in an aqueous medium.
Herbicidal compositions comprising the herbicide N-phosphonomethyl-glycine or derivatives thereof (“glyphosate”), are useful for suppressing the growth of, or killing, unwanted plants such as grasses, weeds and the like. Glyphosate typically is applied to the foliage of the target plant. After application the glyphosate is absorbed by the foliar tissue of the plant and translocated throughout the plant. Glyphosate noncompetitively blocks an important biochemical pathway which is common to virtually all plants, but which is absent in animals. Although glyphosate is very effective in killing or controlling the growth of unwanted plants, the uptake (i.e., absorption) of glyphosate by the plant foliar tissue and translocation of glyphosate throughout the plant is relatively slow. Visual symptoms that a plant has been treated with glyphosate may not appear until one week or more after treatment.
There is a continuing need for herbicidal compositions which exhibit long-term control of unwanted plants and exhibit early visual symptoms of treatment. These compositions would be well suited to applications in cooler temperatures wherein the early visual symptoms may be readily seen while the long-term control would improve as temperatures increase.
As will be clear from the disclosure that follows, these and other benefits are provided by the present invention.